NATURAL-HISTORY AND MANAGEMENT OF THE ASYMPTOMATIC, MODERATELY STENOTIC INTERNAL CAROTID-ARTERY

Purpose: Although it has been widely accepted as the evidence supporti ng prophylactic carotid endarterectomy, aspects of the Asymptomatic Ca rotid Atherosclerosis Study have left unease among clinicians who must decide which individuals without symptoms should undergo surgery. Add itional confusion has been created by the fact that the several large randomized trials investigating the efficacy of carotid endarterectomy have classified and analyzed different categories of carotid stenosis . In an effort to provide more information on the natural history of a symptomatic, moderate carotid artery stenosis (50% to 79%), we have re viewed data on approximately 500 arteries. Methods: Records of our vas cular laboratory from 1990 to 1992 were reviewed. We identified 425 pa tients with asymptomatic, moderate carotid artery stenosis; 71 patient s had bilateral stenoses in this category, resulting in 496 arteries f or study. Results: The mean length of follow-up was 38 +/- 18 months. New ipsilateral strokes occurred in 16 (3.8%) patients. New ipsilatera l transient ischemic attacks occurred in 25 (5.9%) patients. Documente d progression of stenosis occurred in 48 (17%) of the 282 arteries for which a repeat duplex examination was available. Arteries that progre ssed to >80% stenosis were significantly more likely to have caused st rokes than those that remained in the 50% to 79% range (10.4% vs 2.1%, p < 0.02). Conversely, arteries that remained stable in the degree of stenosis were significantly more likely to have remained asymptomatic than those that progressed (92.7% vs 62.5%, p < 0.001). With life-tab le analysis the estimated cumulative ipsilateral stroke rate was 0.85% at 1 year, 3.6% at 3 years, and 5.4% at 5 years. The respective estim ated cumulative transient ischemic attack rates were 1.9%, 5.5%, and 6 .3%. The respective estimated cumulative rates for progression of sten osis were 4.9%, 16.7%, and 26.5%. Life-table comparison of ipsilateral stroke revealed a significantly higher cumulative rate among arteries that progressed in the degree of stenosis than among those that remai ned stable (p < 0.001). Conclusions: Based on the low rate of permanen t neurologic events in these cases, prophylactic carotid endarterectom y for the asymptomatic, moderately stenotic internal carotid artery ca nnot currently be recommended. The only factor that appears to predict increased risk for future stroke is progression of stenosis. Careful follow-up with serial repeat duplex examinations must be performed in these patients. Until there are widely accepted duplex parameters that can provide all clinicians with accurate identification of arteries w ith narrowing corresponding to 60% stenosis as defined by the Asymptom atic Carotid Atherosclerosis Study, all surgeons will need to be aware of specifically how their noninvasive laboratories are deriving their results. For the many laboratories that continue to use the Universit y of Washington criteria, 80% should remain the level above which prop hylactic carotid endarterectomy is warranted.